1. Field of the Invention
This invention relates to sample-to-sample carryover in an automated clinical analyzer, and, more particularly, addressing the problem of sample-to-sample carryover in an automated clinical analyzer by improving the order of execution of assays in a set of assays.
2. Discussion of the Art
A laboratory automation system integrates at least one clinical analyzer with the other components of the system for the purpose of automating the delivery of samples between the at least one clinical analyzer and those other components of the system. The at least one clinical analyzer is typically an automated clinical analyzer. A laboratory automation system can comprise, and preferably does comprise, a plurality of automated clinical analyzers.
It is known that whenever a sample probe of an automated clinical analyzer aspirates a given sample or a portion thereof from a sample container, the sample probe has the potential for contaminating the sample with a small portion of a different sample that had been aspirated previously. This mode of contamination is typically referred to as carryover, more particularly, sample-to-sample carryover. Automated clinical analyzers employ aggressive techniques for washing sample probes, special cleaning solutions for washing sample probes, and large volumes of probe cleaning solutions to minimize this type of carryover. See, for example, United States Patent Application Publication No. 2003/0223472 A1 and United States Patent Application Publication No. 2005/0279387 A1, both of which are incorporated herein by reference. However, because in most cases a sample probe can never be completely cleaned, i.e., to a level at which sample-to-sample carryover is completely eliminated, techniques for cleaning sample probes merely reduce carryover to an acceptable level, as determined by the operator of the automated clinical analyzer or on the basis of the sensitivity of the assay. It is also known that a given assay has a sensitivity threshold. Sensitivity threshold refers to the minimum concentration of analyte in a sample that can be detected or measured or both. Depending on the sensitivity threshold of a particular assay, this sample-to-sample carryover can adversely affect results.
Currently, to avoid the effects of contamination of a sample by sample-to-sample carryover by the sample probe of an automated clinical analyzer in a laboratory automation system, a portion of the sample is aspirated from the original sample container and dispensed into an additional sample container, and a disposable tip is applied to the sample probe prior to aspirating the sample from the additional sample container. This sample transfer step increases costs, because additional sample containers and identifying indicia therefor, such as, for example, barcodes, are required. More importantly, the transfer step delays reporting of results, which could adversely affect the care of a patient. In addition, although disposable tips eliminate sample-to-sample carryover completely, the use of disposable tips is much more costly than merely washing the reusable sample probe between dispensing steps.
If the sample is a STAT sample (i.e., Short Turn Around Time sample) and results from more than one clinical analyzer are required quickly, it may be more expedient to aspirate at least one portion of the sample from the original sample container and dispense that at least one portion into at least one additional sample container, each additional sample container having its own position in the order for execution of an assay. However, additional costs will be incurred for the additional sample containers, additional labels for the additional sample containers, etc.
U.S. Pat. No. 4,971,913 discloses a method of controlling a reagent delivery system for delivering a plurality of different reagents into successive sample-containing reaction vessels in an automatic chemical analyzer for measurement of corresponding tests specimens in a plurality of test items. The method comprises the steps of:                preparing at least one reagent delivery device, the number of which is smaller than that of the reagents of differing kinds;        storing in memory means information representing a predetermined relation between the test items with respect to the influence of contamination between the reagents upon a measurement; and        controlling the operation of the reagent delivery device in accordance with the predetermined relation stored in the memory means in such a manner that the measurement is not affected by the contamination between the reagents.This patent deals solely with contamination by reagents.        
WO 98/45679 discloses a method and apparatus for optimizing the sequence of assays on an automated random access instrument so as to reduce reagent cross-contamination problems. A common vehicle for reagent cross-contamination is the reagent probe surface, which transfers reagents for the various tests. When a plurality of assays are run on a single sample, an initial best path (order of assays) is identified, after which the iterative process of looking for a better alternative begins. This process involves the application of a knowledge base concerning relationships associated with random access cross-contamination, to search the state space. This reference, too, deals with contamination by reagents.
It would be desirable to develop a method whereby the order of execution of assays is integrated with the workflow of the laboratory, additional costs resulting from the use of additional sample containers are minimized, and acceptable response times for STAT samples are still maintained.